全文获取类型
收费全文 | 6703篇 |
免费 | 1188篇 |
国内免费 | 1129篇 |
出版年
2024年 | 91篇 |
2023年 | 269篇 |
2022年 | 384篇 |
2021年 | 480篇 |
2020年 | 380篇 |
2019年 | 387篇 |
2018年 | 328篇 |
2017年 | 302篇 |
2016年 | 325篇 |
2015年 | 276篇 |
2014年 | 412篇 |
2013年 | 427篇 |
2012年 | 299篇 |
2011年 | 332篇 |
2010年 | 232篇 |
2009年 | 274篇 |
2008年 | 350篇 |
2007年 | 381篇 |
2006年 | 338篇 |
2005年 | 268篇 |
2004年 | 278篇 |
2003年 | 252篇 |
2002年 | 212篇 |
2001年 | 176篇 |
2000年 | 123篇 |
1999年 | 146篇 |
1998年 | 137篇 |
1997年 | 114篇 |
1996年 | 124篇 |
1995年 | 132篇 |
1994年 | 108篇 |
1993年 | 93篇 |
1992年 | 71篇 |
1991年 | 75篇 |
1990年 | 53篇 |
1989年 | 52篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 31篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 31篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1974年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有9020条查询结果,搜索用时 15 毫秒
101.
Mitsuo Matsuda Toshiya Nosaka Masaaki Sato Norio Ohshima 《European journal of applied physiology and occupational physiology》1993,66(2):122-126
To evaluate the effects of exercise on aortic wall elasticity and elastic components, young male rats underwent various exercise regimes for 16 weeks. In the exercised rats, the aortic incremental elastic modulus decreased significantly when under physiological strain. The aortic content of elastin increased significantly and the calcium content of elastin decreased significantly in the exercised group. The accumulated data from the exercised and sedentary groups revealed that the elastin calcium content was related positively to the incremental elastic modulus. We concluded that physical exercise from an early age decreases the calcium deposit in aortic wall elastin and that this effect probably produced in the exercised rats a distensible aorta. 相似文献
102.
Renato Baserga 《Molecular reproduction and development》1993,35(4):353-357
103.
Ryuzo Sakakibara Kazuya Sakai Yuko Sakurai Tae Kohnoura Masatsune Ishiguro 《Molecular reproduction and development》1993,34(1):101-106
Mouse oocyte maturation inhibitory factors, on the basis of inhibitory activity of spontaneous germinal vesicle breakdown (GVBD) of denuded mouse oocytes in culture, were extracted and partially purified by reversed-phase resin adsorption and Sephadex G-100 and G-50 column chromatographies from the urine of pregnant women. Denuded oocytes obtained from ovaries of ICR mice underwent spontaneous GVBD by cultivation for 3 h in modified Krebs–Ringer's buffered solution, while this spontaneous GVBD was found to be inhibited by adding the final preparation (U-D-4) of urine. The inhibition was dose dependent, ranging from 0.6 to 10 μg protein/ml medium. Oocytes treated with U-D-4 and resuspended in control medium resumed GVBD. The molecular mass of U-D-4 was estimated to be less than 2,000 Da with gel filtration. Ether treatment failed to extract inhibitory factor(s) from U-D-4 and pepsin treatment inactivated U-D-4, indicating that inhibitory factor(s) in U-D-4 are peptide-like substances. The inhibitory effect of U-D-4 on spontaneous GVBD was partially reversed in the presence of naloxone, a potent opioid antagonist. U-D-4s obtained from urine samples of pregnant women, nonpregnant women, and men showed the inhibitory effect on spontaneous GVBD; however, the activity of U-D-4 obtained from pregnancy urine was significantly more potent than those of the other urine samples. © 1993 Wiley-Liss, Inc. 相似文献
104.
为探究了哥王Wikstroemiaindica的叶功能性状特征及其影响因素,在海岛植被调查的基础上对了哥王叶片进行取样并测定其功能性状指标,利用变异系数法和Pearson相关性分析探讨叶功能性状之间的差异与联系,运用冗余分析研究了哥王叶功能性状对土壤因子的响应。结果表明,了哥王的叶功能性状变异系数介于9.76%~23.73%,其中叶体积变异幅度最大(23.73%),叶干物质含量变异幅度最小(9.76%),整体上了哥王叶功能性状保持相对稳定。了哥王各项叶功能性状之间具有一定的相关性,联系较密切。了哥王叶功能性状主要受土壤中有机质、全氮、碱解氮的影响,土壤中有机质、全氮、碱解氮的含量与比叶面积呈正比,与叶厚度、叶体积成反比。了哥王的叶片可以通过一定的性状变异和组合来适应外部环境的变化,以较好地适应海岛恶劣的环境。该研究结果可为了哥王野生种质资源的保护、利用以及人工栽培提供参考。 相似文献
105.
本文引用Harper(1977)的构件结构理论,从构件结构单位、无性系分株和无性系三个层次,对四川南充市郊慈竹无性系种群的能值特点及其影响能值的计测因素进行了定量研究。研究结果表明:慈竹无性系种群中,各构件单位的去灰分热值(AFCV)分别为:根15349.42J/g、根茎16372.92J/g、秆17106.06J/g、枝18111.99J/g和叶19451.90J/g;慈竹无性系分株的AFCV(J/g)随龄级增大而递增;慈竹无性系水平上的AFCV为:Ⅰ龄占16.47%、Ⅱ龄占25.76%、Ⅲ龄占36.32%、Ⅳ龄为13.08%及Ⅴ龄为8.37%。用恒容燃烧法测定热值时,其能值变化与氧分压密切相关。用经验公式计算的能值较作图法高;用AFCV表示能值较总干重热值(GCV)准确。 相似文献
106.
David G. Thomassen 《In vitro cellular & developmental biology. Animal》1993,29(6):498-504
Summary Factors regulating the proliferation of normal, preneoplastic, and neoplastic rat tracheal epithelial (RTE) cells were investigated
to identify changes taking place during the progression of RTE cells to neoplasia. Normal RTE cells exhibit clonal proliferation
in a serum-free medium containing pituitary extract, serum albumin, cholera toxin, epidermal growth factor, hydrocortisone,
and insulin. All combinations of these six factors were examined for their abilities to support clonal proliferation of normal,
preneoplastic, and neoplastic RTE cells. In general, preneoplastic RTE cells required fewer factors for proliferation than
normal RTE cells, and neoplastic cells required fewer factors than preneoplastic cells. A common pattern of reductions has
been identified in the growth factors required for the clonal proliferation of preneoplastic vs. normal RTE cells and for
neoplastic vs. preneoplastic and normal RTE cells. Normal RTE cells exhibit clonal proliferation in a serum-free medium supplemented
with a minimum of six factors: bovine serum albumin, bovine pituitary extract, cholera toxin, epidermal growth factor, hydrocortisone,
and insulin. Preneoplastic RTE cells exhibit clonal proliferation in a serum-free medium supplemented with four factors: bovine
serum albumin, bovine pituitary extract, hydrocortisone, and insulin. Finally, neoplastic RTE cells exhibit clonal proliferation
in a serum-free medium supplemented with two factors: bovine serum albumin and bovine pituitary extract. These results suggest
that the progression of RTE cells to neoplasia is associated with a series of changes in regulatory pathways that control
cell proliferation. 相似文献
107.
Laetitia Mathon Virginie Marques Stéphanie Manel Camille Albouy Marco Andrello Emilie Boulanger Julie Deter Régis Hocdé Fabien Leprieur Tom B. Letessier Nicolas Loiseau Eva Maire Alice Valentini Laurent Vigliola Florian Baletaud Sandra Bessudo Tony Dejean Nadia Faure Pierre-Edouard Guerin Meret Jucker Jean-Baptiste Juhel Kadarusman Andrea Polanco F. Laurent Pouyaud Dario Schwörer Kirsten F. Thompson Marc Troussellier Hagi Yulia Sugeha Laure Velez Xiaowei Zhang Wenjun Zhong Loïc Pellissier David Mouillot 《Global Ecology and Biogeography》2023,32(8):1336-1352
Aim
Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.Location
Tropical, temperate and polar coastal areas.Time period
Present day.Major taxa studied
Marine fishes.Methods
We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.Results
We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.Main conclusions
Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions. 相似文献108.
109.
Takafumi Tadano Hiroki Otani Masanori Taira Igor B. Dawid 《Genesis (New York, N.Y. : 2000)》1993,14(3):204-211
Mesoderm development in Xenopus laevis depends on inductive cell interactions mediated by diffusible molecules. The mesoderm inducer activin is capable of redirecting the development of animal explants both morphologically and biochemically. We have studied the induction of four regulatory genes, Mix. 1, goosecoid (gsc), Xlim-1 and Xbra in such explants by activin, and the influence of other factors on this induction. Activin induction of gsc is strongly enhanced by dorsalization of the embryo by LiCl, while expression of the other genes is only slightly enhanced. The protein synthesis inhibitor cycloheximide (CHX) inhibits the activin-dependent induction of Xbra partially, while induction of Mix. 1 and Xlim- 1 is essentially unaffected. In contrast, gsc shows strong superinduction in the presence of activin and CHX, and can be induced in animal explants by CHX alone. Induction and superinduction by CHX have previously been observed for immediate early genes in a variety of systems, notably for the activation of c-fos expression by serum stimulation, but have not been reported in early amphibian embryos. © 1993Wiley-Liss, Inc. 相似文献
110.
Identification of tyrosines 154 and 307 in the extracellular domain and 653 and 766 in the intracellular domain as phosphorylation sites in the heparin-binding fibroblast growth factor receptor tyrosine kinase (flg). 总被引:3,自引:0,他引:3 下载免费PDF全文
J. Hou K. McKeehan M. Kan S. A. Carr M. J. Huddleston J. W. Crabb W. L. McKeehan 《Protein science : a publication of the Protein Society》1993,2(1):86-92
Four tyrosine residues have been identified as phosphorylation sites in the tyrosine kinase isoform of the heparin-binding fibroblast growth factor receptor flg (FGF-R1). Baculoviral-insect cell-derived recombinant FGF-R1 was phosphorylated and fragmented with trypsin while immobilized on heparin-agarose beads. Phosphotyrosine peptides were purified by chromatography on immobilized anti-phosphotyrosine antibody and analyzed by Edman degradation and electrospray tandem mass spectrometry. Tyrosine residue 653, which is in a homologous spatial position to major autophosphorylation sites in the catalytic domain of the src and insulin receptor kinases, is the major intracellular FGF-R1 phosphorylation site. Residue 766 in the COOH-terminus outside the kinase domain is a secondary site. Tyrosine residues 154 and 307, which are in the extracellular domain of transmembrane receptor isoforms and are in an unusual sequence context for tyrosine phosphorylation, were also phosphorylated. 相似文献